During a drilling operation, knowledge of the formation surrounding the wellbore may be desirable. Typically, a drill string will include a bottom hole assembly (BHA) which may include sensors positioned to track the progression of the wellbore or measure or log wellbore parameters. In some cases, the BHA may include a measurement while drilling (MWD) or logging while drilling (LWD) system to log downhole parameters. One such measurement is the resistivity of the surrounding formation.
A resistivity measurement measures the resistivity (inverse of conductivity) of the surrounding formation. Because hydrocarbons are generally nonconductive whereas water is, a resistivity measurement may allow a driller to determine the presence or absence of hydrocarbons in the surrounding formation. Resistivity measurements may be made by transmitting a radiofrequency signal into the surrounding formation and receiving the reflections. By measuring, for example, the attenuation and phase shift of the received signal, the resistivity of the surrounding formation may be calculated. However, typical transmission antenna arrangements may induce a portion of the signal into the tool body by capacitive coupling between the transmit antenna and the tool body. In order to alleviate this, complicated and bulky circuitry must be utilized to prevent such capacitive coupling. For example, transformers may be used to drive the antenna with a differential signal centered on the tool body's electric potential. However, the transformer takes up physical space and generates heat. Furthermore, a transformer may limit the ability of the transmission circuit to transmit on multiple frequencies.